1. Field of the Invention
The present invention relates to an electronic keyboard instrument having a speaker box.
2. Description of the Related Art
Conventionally, it has been known to provide an electronic keyboard instrument with a speaker box so as to ensure ample sound volume and produce musical tones with nuances close to those of acoustic piano (see, Japanese Patent Publication No. 3644356).
In the keyboard instrument disclosed in this patent publication, speakers are mounted on an instrument main body so as to be directed upward and open holes are formed in and extend through an enclosure that covers rear surfaces of the speakers, whereby sounds are radiated upwardly and downwardly from the speakers and the open holes. Sounds radiated from the speakers are reflected by a reflector board of the keyboard instrument and transmitted to the audience, whereas sounds passing through the open holes are reflected by the floor and transmitted to the audience.
However, the downward sound radiation in this keyboard instrument made by causing air vibration produced by the upwardly directed speakers to propagate downward via the open holes of the enclosure is insufficient in realizing ample acoustic sounds as provided by a grand piano. In mounting the speaker box on the electronic keyboard instrument, there is a demand to prevent the construction from being complicated.